HIE CARBONIFEROUS SYSTEM 323 



It is doubtless true that from a botanical point of view the 

 Mill.- tone grit of the Pennine area is only the basal portion of the 

 Lower Coal-measures, and that in other areas, such as Bristol and 

 South Wales, the latter might be represented only by sandstonea 

 FuttluT, it is almost certain that the Millstone grit episode marks 

 a general uplift of the whole British region, and a shallowing of 

 all the areas in which deposition was taking place. This uplift 

 may have been greater in some parts of the region than in others, 

 and deposition may possibly have been stopped for a time in 

 Southern England ; but when we pass over into Belgium, and are 

 asked to believe that divisions which have a thickness of 3000 to 

 4000 feet in England are entirely absent in that country, the case 

 is different. There is no stratigraphical evidence of such a break, 

 and if the absence of beds was due to uplift into dry land, signs of 

 such a break should be clear and conspicuous. 



Another and very different explanation presents itself which 

 should be carefully considered by the botanists ; this is that the 

 absence of the species in question may be due to geographical 

 limitation. It may be that the particular assemblage found in the 

 lower stage of the northern region did not extend into the southern 

 region, and that the southern assemblage did not extend into the 

 northern region until the epoch of our Middle Coal-measures. In 

 other words, the deposition of Coal-measures may have been con- 

 temporaneous in both regions throughout Westphalian times, but 

 the succession of plant-assemblages was different in the two regions, 

 and dependent on slight climatal differences north and south of a 

 certain line of latitude. The truth of this theory must be tested 

 by more careful zonal study both of the plants and of the shells. 



REFERENCES 



1 Kidston, Proc. Roy. Phys. Soc., Edin., vol. xii. p. 183. 



2 Gibson, Quart. Journ. Geol. Soc. vol. Ivii. p. 251. 



* Peach and Home, Trans. Edin. Roy. Soc. vol. xl. p. 835 (1903). 



" Geol. of Edinburgh," Mem. Geol. Survey, 2nd ed. (1910). 

 8 Hardman, Mem. Geol. Surv. Ireland, Expl. of Sheet 35. 

 , 6 "Geology of S. Wales Coalfield," Parts vii. and viii., Mem. Geol. Survey. 



7 Ussher, in Proc. Som. Arch, and N.H. Soc. vol. xlvi. p. 1. 



8 Arber, Quart. Journ. Geol. Soc. vol. Ixiii. p. 6 (1907). ; 



9 Zeiller, Bull. Soc. Geol. Fr. (3) xxii. p. 483 (1894). 



10 Feistmantel, Geol. Mag. for 1877, p. 105. 



11 Schellwein, Palceontographica, xxxix. 



